Compositions and methods for preparing oligonucleotide solutions

ABSTRACT

The present invention is directed to methods and compositions for generating a pool of oligonucleotides. The invention finds use in preparing a population or subpopulations of oligonucleotides in solution. The pool of oligonucleotides finds use in a variety of nucleic acid detection and/or amplification assays.

The present application is a continuation of U.S. application Ser. No.09/642,068, filed on Aug. 18, 2000, which claims the benefit of priorityof U.S. Provisional Application No. 60/149,344, filed Aug. 18, 1999,both of which are expressly incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to methods and compositions forgenerating a pool of oligonucleotides. The invention finds use inpreparing a pool of oligonucleotides in solution. The pool ofoligonucleotides finds use in a variety of nucleic acid detection and/oramplification assays.

BACKGROUND OF THE INVENTION

The detection of specific nucleic acids is an important tool fordiagnostic medicine and molecular biology research. Gene probe assayscurrently play roles in identifying infectious organisms such asbacteria and viruses, in probing the expression of normal and mutantgenes and identifying mutant genes such as oncogenes, in typing tissuefor compatibility preceding tissue transplantation, in matching tissueor blood samples for forensic medicine, and for exploring homology amonggenes from different species.

A variety of techniques for the detection of nucleic acids have beendeveloped and include techniques that can be classified as either targetamplification or signal amplification. Target amplification strategiesinclude the polymerase chain reaction (PCR), strand displacementamplification (SDA), and nucleic acid sequence based amplification(NASBA).

Alternatively, rather than amplify the target, alternate techniques usethe target as a template to replicate a signaling probe, allowing asmall number of target molecules to result in a large number ofsignaling probes, that then can be detected. Signal amplificationstrategies include the ligase chain reaction (LCR), cycling probetechnology (CPT), invasive cleavage techniques such as Invader™technology, Q-Beta replicase (QβR) technology, and the use of“amplification probes” such as “branched DNA” that result in multiplelabel probes binding to a single target sequence.

The polymerase chain reaction (PCR) is widely used and described, andinvolves the use of primer extension combined with thermal cycling toamplify a target sequence; see U.S. Pat. Nos. 4,683,195 and 4,683,202,and PCR Essential Data, J. W. Wiley & Sons, Ed. C. R. Newton, 1995, allof which are incorporated by reference. In addition, there are a numberof variations of PCR which also find use in the invention, including“quantitative competitive PCR” or “QC-PCR”, “arbitrarily primed PCR” or“AP-PCR”, “immuno-PCR”, “Alu-PCR”, “PCR single strand conformationalpolymorphism” or “PCR-SSCP”, allelic PCR (see Newton et al. Nucl. AcidRes. 17:2503 91989); “reverse transcriptase PCR” or “RT-PCR”, “biotincapture PCR”, “vectorette PCR”, “panhandle PCR”, and “PCR select cDNAsubtraction”, among others.

Strand displacement amplification (SDA) is generally described in Walkeret al., in Molecular Methods for Virus Detection, Academic Press, Inc.,1995, and U.S. Pat. Nos. 5,455,166 and 5,130,238, all of which arehereby incorporated by reference.

Nucleic acid sequence based amplification (NASBA) is generally describedin U.S. Pat. No. 5,409,818 and “Profiting from Gene-based Diagnostics”,CTB International Publishing Inc., N.J., 1996, both of which areincorporated by reference.

Cycling probe technology (CPT) is a nucleic acid detection system basedon signal or probe amplification rather than target amplification, suchas is done in polymerase chain reactions (PCR). Cycling probe technologyrelies on a molar excess of labeled probe which contains a scissilelinkage of RNA. Upon hybridization of the probe to the target, theresulting hybrid contains a portion of RNA:DNA. This area of RNA:DNAduplex is recognized by RNAseH and the RNA is excised, resulting incleavage of the probe. The probe now consists of two smaller sequenceswhich may be released, thus leaving the target intact for repeatedrounds of the reaction. The unreacted probe is removed and the label isthen detected. CPT is generally described in U.S. Pat. Nos. 5,011,769,5,403,711, 5,660,988, and 4,876,187, and PCT published applications WO95/05480, WO 95/1416, and WO 95/00667, all of which are specificallyincorporated herein by reference.

The oligonucleotide ligation assay (OLA; sometimes referred to as theligation chain reaction (LCR)) involve the ligation of at least twosmaller probes into a single long probe, using the target sequence asthe template for the ligase. See generally U.S. Pat. Nos. 5,185,243,5,679,524 and 5,573,907; EP 0 320 308 B1; EP 0 336 731 B1; EP 0 439 182B1; WO 90/01069; WO 89/12696; and WO 89/09835, all of which areincorporated by reference.

Invader™ technology is based on structure-specific polymerases thatcleave nucleic acids in a site-specific manner. Two probes are used: an“invader” probe and a “signaling” probe, that adjacently hybridize to atarget sequence with a non-complementary overlap. The enzyme cleaves atthe overlap due to its recognition of the “tail”, and releases the“tail” with a label. This can then be detected. The Invader™ technologyis described in U.S. Pat. Nos. 5,846,717; 5,614,402; 5,719,028;5,541,311; and 5,843,669, all of which are hereby incorporated byreference.

“Rolling circle amplification” is based on extension of a circular probethat has hybridized to a target sequence. A polymerase is added thatextends the probe sequence. As the circular probe has no terminus, thepolymerase repeatedly extends the circular probe resulting inconcatamers of the circular probe. As such, the probe is amplified.Rolling-circle amplification is generally described in Baner et al.(1998) Nuc. Acids Res. 26:5073-5078; Barany, F. (1991) Proc. Natl. Acad.Sci. USA 88:189-193; and Lizardi et al. (1998) Nat Genet. 19:225-232,all of which are incorporated by reference in their entirety.

“Branched DNA” signal amplification relies on the synthesis of branchednucleic acids, containing a multiplicity of nucleic acid “arms” thatfunction to increase the amount of label that can be put onto one probe.This technology is generally described in U.S. Pat. Nos. 5,681,702,5,597,909, 5,545,730, 5,594,117, 5,591,584, 5,571,670, 5,580,731,5,571,670, 5,591,584, 5,624,802, 5,635,352, 5,594,118, 5,359,100,5,124,246 and 5,681,697, all of which are hereby incorporated byreference.

Similarly, dendrimers of nucleic acids serve to vastly increase theamount of label that can be added to a single molecule, using a similaridea but different compositions. This technology is as described in U.S.Pat. No. 5,175,270 and Nilsen et al., J. Theor. Biol. 187:273 (1997),both of which are incorporated herein by reference.

Recent focus has been on the analysis of the relationship betweengenetic variation and phenotype by making use of polymorphic DNAmarkers. Previous work utilized short tandem repeats (STRs) aspolymorphic positional markers; however, recent focus is on the use ofsingle nucleotide polymorphisms (SNPs), which occur at an averagefrequency of more than 1 per kilobase in human genomic DNA. Some SNPs,particularly those in and around coding sequences, are likely to be thedirect cause of therapeutically relevant phenotypic variants and/ordisease predisposition. Multiplex PCR amplification of SNP loci withsubsequent hybridization to oligonucleotide arrays has been shown to bean accurate and reliable method of simultaneously genotyping at leasthundreds of SNPs; see Wang et al., Science, 280:1077 (1998); see alsoSchafer et al., Nature Biotechnology 16:33-39 (1998). The compositionsof the present invention facilitate multiplex assays.

There are a variety of particular techniques that are used to detectsequence, including mutations and SNPs. These include, but are notlimited to, ligation based assays, cleavage based assays (mismatch andinvasive cleavage such as Invader™), single base extension methods (seeWO 92/15712, EP 0 371 437 B1, EP 0317 074 B1; Pastinen et al., GenomeRes. 7:606-614 (1997); Syvãnen, Clinica Chimica Acta 226:225-236 (1994);and WO 91/13075), and competitive probe analysis (e.g. competitivesequencing by hybridization; see below).

In addition, DNA sequencing is a crucial technology in biology today, asthe rapid sequencing of genomes, including the human genome, is both asignificant goal and a significant hurdle. Thus there is a significantneed for robust, high-throughput methods. Traditionally, the most commonmethod of DNA sequencing has been based on polyacrylamide gelfractionation to resolve a population of chain-terminated fragments(Sanger et al., Proc. Natl. Acad. Sci. USA 74:5463 (1977); Maxam &Gilbert). The population of fragments, terminated at each position inthe DNA sequence, can be generated in a number of ways. Typically, DNApolymerase is used to incorporate dideoxynucleotides that serve as chainterminators.

Several alternative methods have been developed to increase the speedand ease of DNA sequencing. For example, sequencing by hybridization hasbeen described (Drmanac et al., Genomics 4:114 (1989); Koster et al.,Nature Biotechnology 14:1123 (1996); U.S. Pat. Nos. 5,525,464; 5,202,231and 5,695,940, among others). Similarly, sequencing by synthesis is analternative to gel-based sequencing. These methods add and read only onebase (or at most a few bases, typically of the same type) prior topolymerization of the next base. This can be referred to as “timeresolved” sequencing, to contrast from “gel-resolved” sequencing.Sequencing by synthesis has been described in U.S. Pat. No. 4,971,903and Hyman, Anal. Biochem. 174:423 (1988); Rosenthal, InternationalPatent Application Publication 761107 (1989); Metzker et al., Nucl.Acids Res. 22:4259 (1994); Jones, Biotechniques 22:938 (1997); Ronaghiet al., Anal. Biochem. 242:84 (1996), Nyren et al., Anal. Biochem.151:504 (1985). Detection of ATP sulfurylase activity is described inKaramohamed and Nyren, Anal. Biochem. 271:81 (1999).

Sequencing using reversible chain terminating nucleotides is describedin U.S. Pat. Nos. 5,902,723 and 5,547,839, and Canard and Arzumanov,Gene 11:1 (1994), and Dyatkina and Arzumanov, Nucleic Acids Symp Ser 18;117 (1987). Reversible chain termination with DNA ligase is described inU.S. Pat. No. 5,403,708. Time resolved sequencing is described inJohnson et al., Anal. Biochem. 136:192 (1984). Single molecule analysisis described in U.S. Pat. No. 5,795,782 and Elgen and Rigler, Proc. NatlAcad Sci USA 91(13):5740 (1994), all of which are hereby expresslyincorporated by reference in their entirety.

One promising sequencing by synthesis method is based on the detectionof the pyrophosphate (PPi) released during the DNA polymerase reaction.As nucleotriphosphates are added to a growing nucleic acid chain, theyrelease PPi. This release can be quantitatively measured by theconversion of PPi to ATP by the enzyme sulfurylase, and the subsequentproduction of visible light by firefly luciferase.

Several assay systems have been described that capitalize on thismechanism. See for example WO93/23564, WO 98/28440 and WO98/13523, allof which are expressly incorporated by reference. A preferred method isdescribed in Ronaghi et al., Science 281:363 (1998). In this method, thefour deoxynucleotides (dATP, dGTP, dCTP and dTTP; collectively dNTPs)are added stepwise to a partial duplex comprising a sequencing primerhybridized to a single stranded DNA template and incubated with DNApolymerase, ATP sulfurylase, luciferase, and optionally anucleotide-degrading enzyme such as apyrase. A dNTP is only incorporatedinto the growing DNA strand if it is complementary to the base in thetemplate strand. The synthesis of DNA is accompanied by the release ofPPi equal in molarity to the incorporated dNTP. The PPi is converted toATP and the light generated by the luciferase is directly proportionalto the amount of ATP. In some cases the unincorporated dNTPs and theproduced ATP are degraded between each cycle by the nucleotide degradingenzyme.

In some cases the DNA template is associated with a solid support. Tothis end, there are a wide variety of known methods of attaching DNAs tosolid supports. Recent work has focused on the attachment of bindingligands, including nucleic acid probes, to microspheres that arerandomly distributed on a surface, including a fiber optic bundle, toform high density arrays. See for example PCTs US98/21193, PCTUS99/14387 and PCT US98/05025; WO98150782; and U.S. Ser. Nos.09/287,573, 09/151,877, 09/256,943, 09/316,154, 60/119,323, 09/315,584;all of which are expressly incorporated by reference.

An additional technique utilizes sequencing by hybridization. Forexample, sequencing by hybridization has been described (Drmanac et al.,Genomics 4:114 (1989); U.S. Pat. Nos. 5,525,464; 5,202,231 and5,695,940, among others, all of which are hereby expressly incorporatedby reference in their entirety). In addition, sequencing using massspectrometry techniques has been described; see Koster et al., NatureBiotechnology 14:1123 (1996).

Finally, the use of adapter-type sequences that allow the use ofuniversal arrays has been described in limited contexts; see for exampleChee et al., Nucl. Acid Res. 19:3301 (1991); Shoemaker et al., NatureGenetics 14:450 (1998); Barany, F. (1991) Proc. Natl. Acad. Sci. USA88:189-193, EP 0 799 897 A1 WO 97/31256, all of which are expresslyincorporated by reference.

PCTs US98/21193, PCT US99/14387 and PCT US98/05025; WO98/50782; and U.S.Ser. Nos. 09/287,573, 09/151,877, 09/256,943, 09/316,154, 60/119,323,09/315,584; all of which are expressly incorporated by reference,describe novel compositions utilizing substrates with microspherearrays, which allow for novel detection methods of nucleic acidhybridization.

A common feature of all of these assays and techniques is therequirement for a large number of oligonucleotides. In addition, asmultiplex experiments are performed, solutions containing multiple typesof oligonucleotides must be prepared.

The prior art describes methods of synthesizing oligonucleotides.Generally, synthesis methods can be divided into directed andnon-directed methods. For non-directed, combinatorial methods,bead-based or tea bag synthesis methods have been described using splitand mix procedures. Split and mix synthesis is described in Peptide andPeptidomimetic Libraries, Molecular Biotechnology, Vol. 9, 1998, whichex expressly incorporated herein by reference. A limitation of thismethod is that all combinations of polymers are synthesized.

Alternatively, the prior art describes directed synthesis methods inwhich a particular polymer is separated from other polymers during thesynthesis process. A limitation to this approach is the necessity forseparate reactions and the requirement to mix the polymers together toform pools of oligonucleotides.

Accordingly, it is an object of the present invention to providecompositions and methods for generating a pool of oligonucleotides.

SUMMARY OF THE INVENTION

In accordance with the objects outlined above, the present inventionprovides methods of generating pools of oligonucleotides. The methodsinclude providing a substrate and at least first and second differentoligonucleotides linked to said substrate through first and secondcleavable linkers, respectively. In addition, the method includescleaving the first and second linkers, thereby releasing the first andsecond oligonucleotides from the substrate thereby generating a pool ofoligonucleotides comprising the first and second oligonucleotides.

In an additional aspect the invention includes a method for generating apool of oligonucleotides comprising providing an array comprising asubstrate and a population of oligonucleotides. The population comprisesat least first and second subpopulations. The subpopulations comprise atleast first and second different oligonucleotides of known sequence. Thefirst and second oligonucleotides are immobilized to first and secondbeads, respectively, through first and second cleavable linkers,respectively. The first and second beads are distributed on thesubstrate. Subsequently, the first and second linkers are cleavedthereby releasing the first and second subpopulations from the first andsecond beads, thereby generating a pool of oligonucleotides comprisingthe first and second oligonucleotides.

In an additional aspect the invention includes a method for generating apool of oligonucleotides comprising providing an array comprising asubstrate and a population of oligonucleotides. The population comprisesat least first and second subpopulations. The subpopulations comprise atleast first and second different oligonucleotides of known sequence. Thefirst and second oligonucleotides are immobilized to a chip throughfirst and second cleavable linkers, respectively. The first and secondlinkers are cleaved thereby releasing the first and secondsubpopulations from the chip, thereby generating a pool ofoligonucleotides comprising the first and second oligonucleotides.

In addition the invention includes a composition comprising a substrateand at least first and second different oligonucleotides of knownsequence linked to the substrate through first and second cleavablelinkers, respectively. The composition also includes at least one linkercleaving agent.

In addition the invention includes a kit comprising a substrate and atleast first and second different oligonucleotides of known sequencelinked to the substrate through first and second cleavable linkers,respectively. The kit also includes at least one linker cleaving agent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Depicts an embodiment of a method of generating a pool ofoligonucleotides. Different subpopulations of oligonucleotides 10, 11and 12 are immobilized on a substrate 20 by a cleavable linker 5.Following the addition of a cleavage agent, the oligonucleotides 10, 11and 12 are released into the solution phase.

FIG. 2 depicts an embodiment of a method of generating a pool ofoligonucleotides. Different subpopulations of oligonucleotides 10, 11and 12 are immobilized on a substrate 20 by different cleavable linkers5, 6 and 7. Following the addition of multiple site-specific cleavageagents, the oligonucleotides immobilized by the respective linkers arereleased into the solution phase.

FIG. 3 depicts an embodiment of a method of generating a pool ofoligonucleotides. Different subpopulations of oligonucleotides 10, 12and 13 are immobilized to an association moiety 30 via a linker 5. Theassociation moiety 30 is distributed in wells 21 in the substrate 20.Following the addition of a cleavage agent, the oligonucleotides 10, 11,12 and 13 are released into the solution phase.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to compositions and methods forpreparing oligonucleotide solutions. In particular the inventionincludes preparing an array of oligonucleotides. The oligonucleotidesare attached either directly or indirectly to a substrate through acleavable linker. Upon cleavage of the linker, a pool ofoligonucleotides is formed. Pools of oligonucleotides find use in anumber of solution-phase nucleic acid detection and/or amplificationreactions.

Accordingly the present invention provides compositions and methods forgenerating pools of oligonucleotides. The method includes providing asubstrate and a plurality of oligonucleotides attached to the substrateby a cleavable linker and then cleaving the linker to release theoligonucleotides from the substrate thereby generating a pool ofoligonucleotides.

In one embodiment the oligonucleotide is directly attached to thesubstrate via a cleavable linker. In an alternative embodiment, theoligonucleotide is indirectly attached to the substrate. In thisembodiment, the oligonucleotide is attached to an association moiety viaa linker. The association moiety is then distributed on the substrate.

By “pool” is meant a plurality or more than one solution-phaseoligonucleotide. Preferably, a pool includes two or more differentoligonucleotides. More preferably a pool includes 20 or more differentoligonucleotides. Most preferably a pool includes greater than 50different oligonucleotides.

By “population” herein is meant a plurality of oligonucleotides. In oneembodiment, within the population are separate subpopulations, which canbe a single oligonucleotide or multiple identical oligonucleotides. Thatis, the oligonucleotides within a subpopulation are the same.Alternatively, a subpopulation may be defined by the linker. That is, inthis embodiment, each subpopulation can be defined by the linker used toimmobilize the oligonucleotide to the substrate and/or associationmoiety. That is, in this embodiment, the linkers within a subpopulationare the same. In one embodiment when the linkers within a subpopulationare the same, the oligonucleotides within the subpopulation are thesame: in an alternative embodiment the oligonucleotides within thesubpopulation need not be the same.

By “nucleic acid” or “oligonucleotide” or grammatical equivalents hereinmeans at least two nucleotides covalently linked together. A nucleicacid of the present invention will generally contain phosphodiesterbonds, although in some cases, as outlined below, nucleic acid analogsare included that may have alternate backbones, comprising, for example,phosphoramide (Beaucage et al., Tetrahedron 49(10):1925 (1993) andreferences therein; Letsinger, J. Org. Chem. 35:3800 (1970); Sprinzl etal., Eur. J. Biochem. 81:579 (1977); Letsinger et al., Nucl. Acids Res.14:3487 (1986); Sawai et al, Chem. Lett. 805 (1984), Letsinger et al.,J. Am. Chem. Soc. 110:4470 (1988); and Pauwels et al., Chemica Scripta26:141 91986)), phosphorothioate (Mag et al., Nucleic Acids Res. 19:1437(1991); and U.S. Pat. No. 5,644,048), phosphorodithioate (Briu et al.,J. Am. Chem. Soc. 111:2321 (1989), O-methylphophoroamidite linkages (seeEckstein, Oligonucleotides and Analogues: A Practical Approach, OxfordUniversity Press), and peptide nucleic acid backbones and linkages (seeEgholm, J. Am. Chem. Soc. 114:1895 (1992); Meier et al., Chem. Int. Ed.Engl. 31:1008 (1992); Nielsen, Nature, 365:566 (1993); Carlsson et al.,Nature 380:207 (1996), all of which are incorporated by reference).Other analog nucleic acids include those with positive backbones (Denpcyet al., Proc. Natl. Acad. Sci, USA 92:6097 (1995); non-ionic backbones(U.S. Pat. Nos. 5,386,023, 5,637,684, 5,602,240, 5,216,141 and4,469,863; Kiedrowshi et al., Angew. Chem. Intl. Ed. English 30:423(1991); Letsinger et al., J. Am. Chem. Soc. 110:4470 (1988); Letsingeret al., Nucleoside & Nucleotide 13:1597 (1994); Chapters 2 and 3, ASCSymposium Series 580, “Carbohydrate Modifications in AntisenseResearch”, Ed. Y. S. Sanghui and P. Dan Cook; Mesmaeker et al.,Bioorganic & Medicinal Chem. Lett. 4:395 (1994); Jeffs et al., J.Biomolecular NMR 34:17 (1994); Tetrahedron Lett. 37:743 (1996)) andnon-ribose backbones, including those described in U.S. Pat. Nos.5,235,033 and 5,034,506, and Chapters 6 and 7, ASC Symposium Series 580,“Carbohydrate Modifications in Antisense Research”, Ed. Y. S. Sanghuiand P. Dan Cook. Nucleic acids containing one or more carbocyclic sugarsare also included within the definition of nucleic acids (see Jenkins etat, Chem. Soc. Rev. (1995) pp 169-176). Several nucleic acid analogs aredescribed in Rawls, C & E News Jun. 2, 1997 page 35. All of thesereferences are hereby expressly incorporated by reference. Thesemodifications of the ribose-phosphate backbone may be done to facilitatethe addition of labels, or to increase the stability and half-life ofsuch molecules in physiological environments.

As will be appreciated by those in the art, all of these nucleic acidanalogs may find use in the present invention. In addition, mixtures ofnaturally occurring nucleic acids and analogs can be made.Alternatively, mixtures of different nucleic acid analogs, and mixturesof naturally occurring nucleic acids and analogs may be made.

Particularly preferred are peptide nucleic acids (PNA) which includespeptide nucleic acid analogs, These backbones are substantiallynon-ionic under neutral conditions, in contrast to the highly chargedphosphodiester backbone of naturally occurring nucleic acids. Thisresults in two advantages. First, the PNA backbone exhibits improvedhybridization kinetics. PNAs have larger changes in the meltingtemperature (Tm) for mismatched versus perfectly matched basepairs. DNAand RNA typically exhibit a 2-4′C drop in Tm for an internal mismatch.With the non-ionic PNA backbone, the drop is closer to 7-9′C. Thisallows for better detection of mismatches. Similarly, due to theirnon-tonic nature, hybridization of the bases attached to these backbonesis relatively insensitive to salt concentration.

The nucleic acids may be single stranded or double stranded, asspecified, or contain portions of both double stranded or singlestranded sequence. The nucleic acid may be DNA, both genomic and cDNA,RNA or a hybrid, where the nucleic acid contains any combination ofdeoxyribo- and ribo-nucleotides, and any combination of bases, includinguracil, adenine, thymine, cytosine, guanine, inosine, xathaninehypoxathanine, isocytosine, isoguanine, etc. A preferred embodimentutilizes isocytosine and isoguanine in nucleic acids designed to becomplementary to other probes, rather than target sequences, as thisreduces non-specific hybridization, as is generally described in U.S.Pat. No. 5,681,702. As used herein, the term “nucleoside” includesnucleotides as well as nucleoside and nucleotide analogs, and modifiednucleosides such as amino modified nucleosides. In addition,“nucleoside” includes non-naturally occurring analog structures. Thusfor example the individual units of a peptide nucleic acid, eachcontaining a base, are referred to herein as a nucleoside.

The oligonucleotides can be of any length although in a preferredembodiment they are from 2 to 200 nucleotides in length, in a preferredembodiment they are from 5 to 100 nucleotides in length and in aparticularly preferred embodiment they are from 7 to 50 nucleotides inlength.

In a preferred embodiment the oligonucleotide is attached to thesubstrate via linker. That is, when attached to a substrate orassociation moiety, the oligonucleotide is bound or conjugated to acleavable linker. By “cleavable linker” is meant a linker that issusceptible to cleavage with a specific agent and mediates binding ofthe substrate and/or the association moiety to the oligonucleotide. Inone embodiment the linker is part of the nucleic acid. Alternatively,the linker can be a modification of the nucleic acid. Alternatively, thelinker is an additional moiety.

Generally, the linker is separable or distinct from the region of themolecule comprising the desired oligonucleotide. That is, upon cleavageof the linker, the nature i.e. structure or sequence of the desiredoligonucleotide is not altered. However, in some embodiments thestructure or sequence of the oligonucleotide is altered.

In one embodiment the oligonucleotide is linked directly to a substratethrough the linker. In an alternative embodiment the oligonucleotide isindirectly linked to the substrate, for example by attachment of thelinker to a bead.

A cleavable linker is susceptible to cleavage with agents such as butnot limited to light, base, acid and enzymes such as sequence specificrestriction enzymes or proteases. In a preferred embodiment the linkeris a nucleotide linker and comprises a site for cleavage by a sequencespecific restriction endonuclease. In an additionally preferredembodiment the restriction site is a substrate for a “rare-cutting”enzyme. Rare-cutting restriction endonucleases are known in the art andinclude, for example, those enzymes that recognize 6 or morenucleotides. In some instances it is preferable to use more frequentrestriction sites such as those that contain a 2, 3, 4 or 5 nucleotiderecognition sequence.

In a preferred embodiment when the linker is an oligonucleotide, thelinker sequences do not have significant homology to the oligonucleotideto which they are attached. That is, the linker sequences aresubstantially unique relative to the oligonucleotides. Thus, in thisembodiment, the linker sequences can be specifically cleaved relative tothe oligonucleotides. Cleavage of the linker results in release of theoligonucleotides into the solution-phase to form a pool ofoligonucleotides.

Accordingly, preferred embodiments utilize some method to select usefullinker sequences. Such methods include the use of computer searching orcomparison programs to find unique cleavage sequences relative to theoligonucleotide sequence. Sequence comparisons are known in the art andinclude, but are not limited to, the local homology algorithm of Smith &Waterman, Adv. Appl. Math. 2:482 (1981), by the homology alignmentalgorith of Needleman & Wunsch, J. Mol. Biool. 48:443 (1970), by thesearch for similarity method of Pearson & Lipman, PNAS USA 85:2444(1988), by computerized implementations of these algorithms (GAP,BESTFIT, FASTA, and TFASTA in the Wisconsin Genetics Software Package,Genetics Computer Group, 575 Science Drive, Madison, Wis.), the Best Fitsequence program described by Devereux et al., Nucl. Acid Res.12:387-395 (1984), preferably using the default settings, or byinspection.

The linker sequences are added to the oligonucleotides in a variety ofways, as will be appreciated by those in the art. In one embodiment, thelinker sequence and oligonucleotide are synthesized contiguously. Thatis, using standard oligonucleotide synthesis methods, theoligonucleotide and linker are synthesized as one continuousoligonucleotide.

In an alternative embodiment, nucleic acid amplification reactions aredone, as is generally outlined in “Detection of Nucleic AcidAmplification Reactions Using Bead Arrays” and “Sequence Determinationof Nucleic Acids using Arrays with Microspheres” both of which werefiled on Oct. 22, 1999, (U.S. Ser. Nos. 60/161,148 and 09/425,633,respectively), and “Detection of Nucleic Acid Reactions on Bead Arrays”filed on Apr. 20, 2000, and Apr. 21, 2000 (U.S. Ser. Nos. 09/553,993 and09/556,463, respectively), all of which are hereby incorporated byreference in their entirety. In general, the techniques can be describedas follows. Most amplification techniques require one or more primershybridizing to the target sequence. The linker sequences can be added toone or more primers that are complementary to the oligonucleotide towhich the linker is to be added (depending on theconfiguration/orientation of the system and need) and the amplificationreactions are run. Thus, for example, PCR primers comprising at leastone linker sequence may be used.

In an alternative embodiment, non-nucleic acid reactions are used to addlinker sequences to the oligonucleotides. In this embodiment, bindingpartner pairs or chemical methods may be used. For example, one memberof a binding partner pair may be attached to the linker sequence and theother member attached to the oligonucleotide. For example, the bindingpartner can be a hapten or antigen, which will bind its binding partner.For example, suitable binding partner pairs include, but are not limitedto: antigens (such as proteins (including peptides)) and antibodies(including fragments thereof (FAbs, etc.)); proteins and smallmolecules, including biotin/streptavidin and digoxygenin and antibodies;enzymes and substrates or inhibitors; other protein-protein interactingpairs; receptor-ligands; and carbohydrates and their binding partners,are also suitable binding pairs. Nucleic acid—nucleic acid bindingproteins pairs are also useful. Preferred binding partner pairs include,but are not limited to, biotin (or imino-biotin) and streptavidin,digeoxinin and Abs, and Prolinx™ reagents.

In a preferred embodiment, chemical attachment methods are used. In thisembodiment, chemical functional groups on each of the oligonucleotidesand linker sequences are used. As is known in the art, this may beaccomplished in a variety of ways. Preferred functional groups forattachment are amino groups, carboxy groups, oxo groups and thiolgroups, with amino groups being particularly preferred. Using thesefunctional groups, the two sequences are joined together; for example,amino groups on each nucleic acid may be attached, for example usinglinkers as are known in the art; for example, homo- orhetero-bifunctional linkers as are well known (see 1994 Pierce ChemicalCompany catalog, technical section on cross-linkers, pages 155-200,incorporated herein by reference).

In a preferred embodiment, aptamers are used in the system. Aptamers arenucleic acids that can be made to bind to virtually any target; see Bocket al., Nature 355:564 (1992); Femulok et al., Current Op. Chem. Biol.2:230 (1998); and U.S. Pat. Nos. 5,270,163, 5,475,096, 5,567,588,5,595,877, 5,637,459, 5,683,867, 5,705,337, and related patents, all ofwhich are expressly incorporated herein by reference.

In one embodiment linkers are added prior to immobilization to thesubstrate and/or bead. That is, a linker-conjugated or linker-boundoligonucleotide is attached to the substrate or association moiety. Inan alternative embodiment, the oligonucleotide is attached to the linkerwhile the linker is immobilized to the substrate or association moiety.Accordingly, when describing attachment of nucleic acids to a substrateor association moiety and attachment of linker-bound orlinker-conjugated oligonucleotides to a substrate or association moietyit is understood that linkers mediate the attachment.

In addition, the present invention is directed to the use of linkersequences to assemble arrays comprising other molecules. That is,cleavable linkers can be used to assemble arrays of molecules other thanoligonucleotides. Other molecules include but are not limited to otherpolymers. Thus, upon cleavage of the linker, pools of solution-phasepolymers are generated. Such polymers include but are not limited topeptides, polysaccharides, polymers of small molecules and the like.

In an alternative embodiment the linker comprises amino acids and thusforms a peptide linker. Peptide linkers are cleaved by agents thatinclude but are not limited to proteases or chemicals including bases,acids or CNBr.

In one embodiment, the oligonucleotides comprise labels. By “label” or“detectable label” herein is meant a moiety that allows detection. Thismay be a primary label or a secondary label. Accordingly, detectionlabels may be primary labels (i.e. directly detectable) or secondarylabels (indirectly detectable).

In a preferred embodiment, the detection label is a primary label. Aprimary label is one that can be directly detected, such as afluorophore. In general, labels fall into three classes: a) isotopiclabels, which may be radioactive or heavy isotopes; b) magnetic,electrical, thermal labels; and c) colored or luminescent dyes. Labelscan also include enzymes (horseradish peroxidase, etc.) and magneticparticles. Preferred labels include chromophores or phosphors but arepreferably fluorescent dyes. Suitable dyes for use in the inventioninclude, but are not limited to, fluorescent lanthanide complexes,including those of Europium and Terbium, fluorescein, rhodamine,tetramethylrhodamine, eosin, erythrosin, coumarin, methyl-coumarins,quantum dots (also referred to as “nanocrystals”: see U.S. Ser. No.09/315,584, hereby incorporated by reference), pyrene, Malacite green,stilbene, LUCIFER YELLOW, CASCADE BLUE, TEXAS RED, Cy dyes (CY3, CY5,etc.), alexa dyes, phycoerythin, bodipy, and others described in the 6thEdition of the Molecular Probes Handbook by Richard P. Haugland, herebyexpressly incorporated by reference.

In a preferred embodiment, a secondary detectable label is used. Asecondary label is one that is indirectly detected; for example, asecondary label can bind or react with a primary label for detection,can act on an additional product to generate a primary label (e.g.enzymes), or may allow the separation of the compound comprising thesecondary label from unlabeled materials, etc. Secondary labels findparticular use in systems requiring separation of labeled and unlabeledprobes, such as SBE, OLA, invasive cleavage reactions, etc; in addition,these techniques may be used with many of the other techniques describedherein. Secondary labels include, but are not limited to, one of abinding partner pair; chemically modifiable moieties; nucleaseinhibitors, enzymes such as horseradish peroxidase, alkalinephosphatases, lucifierases, etc.

In a preferred embodiment, the secondary label is a binding partnerpair. For example, the label may be a hapten or antigen, which will bindits binding partner. For example, suitable binding partner pairsinclude, but are not limited to: antigens (such as proteins (includingpeptides)) and antibodies (including fragments thereof (FAbs, etc.));proteins and small molecules, including biotin/streptavidin; enzymes andsubstrates or inhibitors; other protein-protein interacting pairs;receptor-ligands; and carbohydrates and their binding partners. Nucleicacid—nucleic acid binding proteins pairs are also useful. Preferredbinding partner pairs include, but are not limited to, biotin (orimino-biotin) and streptavidin, digeoxinin and Abs, and PROLINX reagents(see www.prolinxinc.com/ie4/home.hmtl).

In a preferred embodiment, the binding partner pair comprises biotin orimino-biotin and streptavidin. Imino-biotin is particularly preferred asimino-biotin disassociates from streptavidin in pH 4.0 buffer whilebiotin requires harsh denaturants (e.g. 6 M guanidinium HCI, pH 1.5 or90% formamide at 95° C.).

In a preferred embodiment, the binding partner pair comprises a primarydetection label and an antibody that will specifically bind to theprimary detection label. By “specifically bind” herein is meant that thepartners bind with specificity sufficient to differentiate between thepair and other components or contaminants of the system, The bindingshould be sufficient to remain bound under the conditions of the assay,including wash steps to remove non-specific binding. In someembodiments, the dissociation constants of the pair will be less thanabout 10⁻⁴-10⁻⁶ M⁻¹, with less than about 10⁻⁵ to 10⁻⁹ M⁻¹ beingpreferred and less than about 10⁻⁷-10⁻⁹ M⁻¹ being particularlypreferred.

In a preferred embodiment, the secondary label is a chemicallymodifiable moiety. In this embodiment, labels comprising reactivefunctional groups are incorporated into the nucleic acid. The functionalgroup can then be subsequently labeled with a primary label. Suitablefunctional groups include, but are not limited to, amino groups, carboxygroups, maleirnide groups, oxo groups and thiol groups, with aminogroups and thiol groups being particularly preferred. For example,primary labels containing amino groups can be attached to secondarylabels comprising amino groups, for example using linkers as are knownin the art; for example, home- or hetero-bifunctional linkers as arewell known (see 1994 Pierce Chemical Company catalog, technical sectionon cross-linkers, pages 155-200, incorporated herein by reference).

Thus, when labeled oligonucleotides are synthesized on an array orsynthesized and associated with a substrate, labeled arrays are formed.In a preferred embodiment, each member of a population ofoligonucleotides is labeled with the same label. In an alternativeembodiment each member of a subpopulation of oligonucleotides is labeledwith the same label. That is, in making the labeled array, the labelserves to identify the oligonucleotide to which it is attached. In asense, the label serves as a code for the sequence of theoligonucleotide.

In a preferred embodiment, the oligonucleotide is attached directly tothe substrate as is described in more detail herein. Alternatively, theoligonucleotide is indirectly associated with the substrate. That is,the oligonucleotide associates with the substrate via an associationmoiety as described herein.

By “substrate” or “solid support” or other grammatical equivalentsherein is meant any material that can be modified for the attachment orassociation of nucleic acids. As will be appreciated by those in theart, the number of possible substrates is very large. Possiblesubstrates include, but are not limited to, glass and modified orfunctionalized glass, plastics (including acrylics, polystyrene andcopolymers of styrene and other materials, polypropylene, polyethylene,polybutylene, polyurethanes, Teflon, etc.), polysaccharides, nylon ornitrocellulose, resins, silica or silica-based materials includingsilicon and modified silicon, carbon, metals, inorganic glasses,plastics, optical fiber bundles, and a variety of other polymers.

By “association moiety” (AM) is meant any material to which anoligonucleotide can be attached that serves as an intermediate forassociation of an oligonucleotide to a substrate. As will be appreciatedby those in the art, the number of possible AMs is large. Possible AMsinclude any number of solid supports such as beads or microspheres.

Generally the substrate is flat (planar), although as will beappreciated by those in the art, other configurations of substrates maybe used as well; for example, when oligonucleotides are associated withthe substrate via a bead as described below, three dimensionalconfigurations can be used, for example by embedding the beads in aporous block of plastic that allows sample or reagent access to thebeads. Similarly, the beads may be placed on the inside surface of atube, for flow-through sample analysis to minimize sample or reagentvolume. Preferred substrates include optical fiber bundles as discussedbelow, and flat planar substrates such as glass, polystyrene and otherplastics and acrylics.

In a preferred embodiment the substrate is a chip or biochip. By “chip”or “biochip” herein is meant a planar substrate to which nucleic acidsare directly or indirectly attached. In a preferred embodiment, thesurface of the biochip and the nucleic acid may be derivatized withchemical functional groups for subsequent attachment of the two. Thus,for example, the biochip is derivatized with a chemical functional groupincluding, but not limited to, amino groups, carboxy groups, oxo groupsand thiol groups, with amino groups being particularly preferred. Usingthese functional groups, the oligonucleotides can be attached usingfunctional groups on the oligonucleotides. For example, nucleic acidscontaining amino groups can be attached to surfaces comprising aminogroups, for example using linkers as are known in the art; for example,homo- or hetero-bifunctional linkers as are well known (see 1994 PierceChemical Company catalog, technical section on cross-linkers, pages155-200, incorporated herein by reference). in addition, in some cases,additional linkers, such as alkyl groups (including substituted andheteroalkyl groups) may be used.

In one embodiment, the substrate is an optical fiber bundle or array, asis generally described in U.S. Ser. Nos. 08/944,850 and 08/519,062, PCTUS98/05025, and PCT US98/09163, all of which are expressly incorporatedherein by reference. Preferred embodiments utilize preformed unitaryfiber optic arrays. By “preformed unitary fiber optic array” herein ismeant an array of discrete individual fiber optic strands that areco-axially disposed and joined along their lengths. The fiber strandsare generally individually clad. However, one thing that distinguished apreformed unitary array from other fiber optic formats is that thefibers are not individually physically manipulatable; that is, onestrand generally cannot be physically separated at any point along itslength from another fiber strand.

In one embodiment at least one surface of the substrate is modified tocontain discrete, individual sites for later association of nucleicacids or oligonucleotides. These sites may comprise physically alteredsites, i.e. physical configurations such as wells or small depressionsin the substrate that can retain AMs such as beads, such that amicrosphere can rest in the well, or the use of other forces (magneticor compressive), or chemically altered or active sites, such aschemically functionalized sites, electrostatically altered sites,hydrophobically/hydrophilically functionalized sites, spots of adhesive,etc.

The sites may be arranged in a pattern, i.e. a regular design orconfiguration, or randomly distributed. A preferred embodiment utilizesa regular pattern of sites such that the sites may be addressed in theX-Y coordinate plane. “Pattern” in this sense includes a repeating unitcell, preferably one that allows a high density of nucleic acids on thesubstrate. However, it should be noted that these sites may not bediscrete sites. That is, it is possible to use a uniform surface ofadhesive or chemical functionalities, for example, that allows theattachment of nucleic acids at any position. That is, the surface of thesubstrate is modified to allow attachment of the nucleic acids atindividual sites, whether or not those sites are contiguous ornon-contiguous with other sites. Thus, the surface of the substrate maybe modified such that discrete sites are formed that can retain a singlenucleic acid, or alternatively, the surface of the substrate is modifiedand nucleic acids, for example, when attached to beads may be placedanywhere, but eventually end up at discrete sites.

In a preferred embodiment, the surface of the substrate is modified tocontain wells, i.e. depressions in the surface of the substrate. Thismay be done as is generally known in the art using a variety oftechniques, including, but not limited to, photolithography, stampingtechniques, molding techniques and microetching techniques. As will beappreciated by those in the art, the technique used will depend on thecomposition and shape of the substrate and the nature of any associationmoieties to be used, if any.

In a preferred embodiment, physical alterations are made in a surface ofthe substrate to produce the sites. In a preferred embodiment, thesubstrate is a fiber optic bundle and the surface of the substrate is aterminal end of the fiber bundle, as is generally described in U.S. Pat.No. 6,023,540 and U.S. Ser. No. 09/151,877, both of which are herebyexpressly incorporated by reference. In this embodiment, wells are madein a terminal or distal end of a fiber optic bundle comprisingindividual fibers. In this embodiment, the cores of the individualfibers are etched, with respect to the cladding, such that small wellsor depressions are formed at one end of the fibers. The required depthof the wells will depend on the size of the moiety i.e. beads, to beadded to the wells.

Generally in this embodiment, the microspheres or beads arenon-covalently associated in the wells, although the wells mayadditionally be chemically functionalized as is generally describedbelow, cross-linking agents may be used, or a physical barrier may beused, i.e. a film or membrane over the beads.

By “microspheres” or “beads” or “particles” or grammatical equivalentsherein is meant small discrete particles. The composition of the beadswill vary, depending on the class of oligonucleotide and the method ofsynthesis. Suitable bead compositions include those used in peptide,nucleic acid and organic moiety synthesis, including, but not limitedto, plastics, ceramics, glass, polystyrene, methylstyrene, acrylicpolymers, paramagnetic materials, thoria sal, carbon graphite, titaniumdioxide, latex or cross-linked dextrans such as Sepharose, cellulose,nylon, cross-linked micelles and Teflon may all be used. “MicrosphereDefection Guide” from Bangs Laboratories, Fishers Ind. is a helpfulguide.

The beads need not be spherical; irregular particles may be used. Inaddition, the beads may be porous, thus increasing the surface area ofthe bead available for either capture probe attachment or tagattachment. The bead sizes range from nanometers, i.e. 100 nm, tomillimeters, i.e. 1 mm, with beads from about 0.2 micron to about 200microns being preferred, and from about 0.5 to about 5 micron beingparticularly preferred, although in some embodiments smaller beads maybe used.

It should be noted that when beads are used, a key component of theinvention is the use of a substrate/bead pairing that allows theassociation or attachment of the beads at discrete sites on the surfaceof the substrate, such that the beads do not move or dislodge during thecourse of the assembly or cleavage.

Attachment of the nucleic acids to the substrate may be done in avariety of ways, as will be appreciated by those in the art, including,but not limited to, chemical or affinity capture (for example, includingthe incorporation of derivatized nucleotides such as AminoLink orbiotinylated nucleotides that can then be used to attach the nucleicacid to a surface, as well as affinity capture by hybridization),cross-linking, and electrostatic attachment, etc. In a preferredembodiment, affinity capture is used to attach the nucleic acids to thesubstrate. For example, nucleic acids can be derivatized, for examplewith one member of a binding pair, and the substrate or associationmoiety derivatized with the other member of a binding pair. Suitablebinding pairs include complementary nucleic acids. In addition, thenucleic acids may be biotinylated (for example using enzymaticincorporate of biotinylated nucleotides, for by photoactivatedcross-linking of biotin). Biotinylated nucleic acids can then becaptured on streptavidin-coated substrate or beads, as is known in theart. Similarly, other hapten-receptor combinations can be used, such asdigoxigenin and antiwdigoxigenin antibodies. Alternatively, chemicalgroups can be added in the form of derivatized nucleotides, that canthem be used to add the nucleic acid to the surface.

In this embodiment, the oligonucleotides are previously synthesized asis known in the art, and then attached to the surface of the solidsupport. As will be appreciated by those skilled in the art, either the5′ or 3′ terminus may be attached to the solid support, or attachmentmay be via an internal nucleoside.

Preferred attachments are covalent, although even relatively weakinteractions (i.e. non-covalent) can be sufficient to attach a nucleicacid to a surface. Thus, for example, electrostatic interactions can beused for attachment, for example by having substrates carrying theopposite charge to the oligonucleotide.

Similarly, affinity capture utilizing hybridization can be used toattach nucleic acids to substrates or association moieties. For example,as is known in the art, polyA+RNA is routinely captured by hybridizationto oligo-dT beads; this may include oligo-dT capture followed by across-linking step, such as psoralen crosslinking). If the nucleic acidsof interest do not contain a polyA tract, one can be attached bypolymerization with terminal transferase, or via ligation of an oligoAlinker, as is known in the art.

Alternatively, chemical crosslinking may be used to attach nucleic acidsto the substrate, for example by photoactivated crosslinking ofthymidine to reactive groups, as is known in the art.

In a preferred embodiment, the surface of the substrate is modified tocontain chemically modified sites, that can be used to attach, eithercovalently or non-covalently, the nucleic acids of the invention to thediscrete sites or locations on the substrate. “Chemically modifiedsites” in this context includes, but is not limited to, the addition ofa pattern of chemical functional groups including amino groups, carboxygroups, oxo groups and thiol groups, that can be used to attach nucleicacids, which generally also contain corresponding reactive functionalgroups; the addition of a pattern of charged groups (similar to thechemical functionalities) for the electrostatic attachment of thenucleic acids, i.e. when the nucleic acids comprise charged groupsopposite to the sites. As outlined above, “pattern” in this senseincludes the use of a uniform treatment of the surface to allowattachment of the nucleic acids at discrete sites, as well as treatmentof the surface resulting in discrete sites. As will be appreciated bythose in the art, this may be accomplished in a variety of ways.

Alternatively, the oligonucleotides may be synthesized in situ on thesubstrate, as is known in the art. For example, photoactivationtechniques utilizing photopolymerization compounds and techniques areused. In a preferred embodiment, the nucleic acids can be synthesized insitu using well known photolithographic techniques, such as thosedescribed in WO 95/25116; WO 95/35505; U.S. Pat. Nos. 5,700,637 and5,445,934; and references cited within, all of which are expresslyincorporated by reference; these methods of attachment form the basis ofthe Affymetrix GENECHIP technology.

Alternatively, the oligonucleotides may be synthesized on the substrateusing printing technology as described in U.S. Pat. No. 5,831,070, whichis expressly incorporated herein by reference. Alternatively, theoligonucleotides may be synthesized by spotting as described in U.S.Pat. No. 5,807,522 which is expressly incorporated herein by reference.

In an alternative embodiment the oligonucleotides are synthesized onassociation moieties or solid support such as microspheres that are thendistributed on a substrate. As is known in the art, many classes ofchemical compounds are currently synthesized on solid supports, such aspeptides, organic moieties, and nucleic acids. It is a relativelystraightforward matter to adjust the current synthetic techniques to usebeads.

In one embodiment the oligonucleotides are synthesized randomly i.e.with no bias or restriction at any of the positions in theoligonucleotide. That is, synthesis is non-directed. As such, poolscomprising random oligonucleotides are generated by the method. Methodsof randomly synthesizing oligonucleotides are known in the art and asdescribed in U.S. Pat. No. 5,504,190, which is expressly incorporatedherein by reference. Other combinatorial techniques are summarized inPeptide and Peptidomimetic Libraries, Molecular Biotechnology, Vol. 9,1998, which ex expressly incorporated herein by reference.

In an alternative embodiment, the oligonucleotides are not randomlyproduced, but rather are synthesized with an eye to targeting aparticular molecule. That is, synthesis of the oligonucleotides isdirected. As is known in the art, oligonucleotides hybridize with acomplementary strand; thus, the oligonucleotides are designed to targeta particular complementary molecule. This complementarity need not beperfect; there may be any number of base pair mismatches that willinterfere with hybridization between the target sequence and the singlestranded nucleic acids of the present invention. However, if the numberof mutations is so great that no hybridization can occur under even theleast stringent of hybridization conditions, the sequence is not acomplementary target sequence. Thus, by “substantially complementary”herein is meant that the probes are sufficiently complementary to thetarget sequences to hybridize under the selected reaction conditions.

In one embodiment oligonucleotides are designed to hybridize with DNA,for example, for genotyping, single nucleotide polymorphism (SNP)detection or for use as primers in amplification, in particularmultiplex amplification, reactions.

Alternatively, oligonucleotides are synthesized with only certaindegenerate positions. That is, some of the positions are fixed or biasedfor a particular nucleotide while other positions are degenerate orsynthesized with random nucleotides.

Accordingly the present invention provides array compositions comprisinga substrate comprising oligonucleotides and a linker. By “array” hereinis meant a plurality of nucleic acids in an array format; the size ofthe array will depend on the composition and end use of the array.Nucleic acids arrays are known in the art, and can be classified in anumber of ways; both ordered arrays (e.g, the ability to resolvechemistries at discrete sites), and random arrays are included. Orderedarrays include, but are not limited to, those made usingphotolithography techniques (Affymetrix GeneChip™), spotting techniques(Synteni and others), printing techniques (Hewlett Packard and Rosetta),three dimensional “gel pad” arrays, etc.

In a preferred embodiment the array compositions further comprise alinker cleaving agent. As described herein, linker cleaving agentsinclude but are not limited to light, chemicals including base and acid,enzymes such as proteases and nucleases. In a particularly preferredembodiment the nucleases include sequence specific restrictionendonucleases as are known in the art and described herein. Additionalcleavage agents are described in Promega Catalog, 1997, pp. 293-297 and34-74, and Pierce Catalog and Handbook, 1994, pp. 0-209 to 0-221, bothof which are expressly incorporated herein by reference.

In an additional embodiment, the compositions further comprisesolution-phase oligonucleotides. That is, once cleavage of the linkerhas begun and the oligonucleotides are cleaved from the substrate, theoligonucleotides are released into the solution-phase. Accordingly, apool of oligonucleotides in solution is formed.

Once formed, the array of oligonucleotides finds use in a number ofaspects. In a particularly preferred embodiment the arrays are contactedwith a cleaving agent that cleaves the linker. That is, the substrate towhich the population oligonucleotides is attached is contacted with acleaving agent thereby releasing the oligonucleotides into the solutionphase (FIG. 1). As one of ordinary skill in the art appreciates cleavageconditions will vary with the nature of the cleavage agent. Generally,when cleavage agents are enzymes, conditions will vary with respect tometal, temperature, pH and salt concentration. The duration or time ofcleavage reactions also will vary depending on the cleavage agentselected.

In an alternative embodiment, the cleaving agent recognizes only asubset of linkers. That is, as described above, each subpopulation ofoligonucleotides contains a different linker. Accordingly, incubation ofthe array with a particular site-specific cleaving agent results inrelease of only the oligonucleotide immobilized with the respectivelinker (FIG. 2). Moreover, incubation with multiple site-specificcleaving agents results in the release of multiple subpoputations ofoligonucleotides.

In an alternative embodiment, the oligonucleotides are indirectlyattached to the substrate. That is, linkers can immobilize theoligonucleotides either directly to the substrate or indirectly. Whenindirectly attached to the substrate, oligonucleotides are attached toAMs via linkers as outlined herein. The AMs are distributed on thesubstrate forming an array. Subsequently, the array is contacted with acleaving agent as described herein resulting in the release of theoligonucleotides into the solution phase (FIG. 3).

In an additional embodiment, the array of oligonucleotides finds use inkits. That is, kits can be formulated to include an array ofoligonucleotides. As described herein, the oligonucleotides may compriserandom oligonucleotides; alternatively, the oligonucleotides maycomprise known sequences. In addition, the oligonucleotides may comprisea label. In this embodiment, the kit comprises a labeled array.

The kit also includes a linker cleaving agent. That is, to facilitatethe formation of a pool of oligonucleotides, the kit includes at leastone but may also include as many cleaving agents as necessary to releasethe desired oligonucleotides from the substrate.

In addition, the kit may also include at least one controloligonucleotide. The control oligonucleotide is designed to becomplementary to a subpopulation of immobilized oligonucleotides or apopulation of control immobilized oligonucleotides. In a preferredembodiment the control oligonucleotide comprises a label as describedherein.

In one embodiment the control oligonucleotide finds use in determiningthe quality of the array of oligonucleotides, That is, in oneembodiment, the control oligonucleotide is contacted with the array ofoligonucteotides prior to cleavage of the linkers. The labeled controloligonucleotide is then detected, for example by viewing the array undera microscope. Other detection methods are described in more detail inU.S. Ser. No. 09/556,463, filed Apr. 21, 2000, which is expresslyincorporated herein by reference. The presence of the label provides anindication of the quality or identity of the array. As such, the arrayof oligonucleotides also facilitates sample handling, tracking andstorage.

Once formed, the pool of oligonucleotides finds use in a number ofassays. In addition, as nucleic acid experiments are performed inmultiplex, a solution that contains many types of oligonucleotides mustbe prepared. Examples of experiments that may require pools ofoligonucleotides when performed in solution include assays forgenotyping, such as OIA, Single Base Extension, Invader and the like,assays for the detection of single nucleotide polymorphisms, sequencing,multiplex amplification including polymerase chain reactions, and thelike.

Preferably, the assays are conducted in solution. Once the solutionphase is performed, the experiments may include an array detection step.Arrays for detecting nucleic acids and nucleic acid reactions are morefully described in U.S. Ser. No. 09/556,463, filed Apr. 21, 2000, whichis expressly incorporated herein by reference.

Pools of oligonucleotides find use in decoding arrays as described inmore detail in U.S. Ser. No. 09/344,526, and U.S. Ser. No. 09/574, 117,both of which are expressly incorporated herein by reference. Inaddition, pools of oligonucleotides find use in microfluidic systems asdescribed in U.S. Ser. No. 09/306,369 which is expressly incorporatedherein by reference. In addition, pools of oligonucleotides find use incomposite array systems as described in U.S. Ser. No. 09/606,369, whichis expressly incorporated herein by reference.

All references cited herein are incorporated by reference in theirentirety.

We claim:
 1. A method of detecting the presence of target nucleic acidscomprising: a) obtaining a pool of greater than 50 different singlestranded oligonucleotides, wherein said pool of oligonucleotides hasbeen produced by: (i) synthesizing greater than 50 different singlestranded oligonucleotides on discrete sites of a first substrate,wherein each of the different single stranded oligonucleotides has adifferent sequence, and (ii) releasing said greater than 50 differentsingle stranded oligonucleotides from said first substrate to generatesaid pool of greater than 50 different single stranded oligonucleotides;b) contacting said pool of greater than 50 different single strandedoligonucleotides with a composition comprising target nucleic acids,whereby said target nucleic acids hybridize with greater than 50different single stranded oligonucleotides in said pool ofoligonucleotides; c) capturing said greater than 50 different singlestranded oligonucleotides in said pool of oligonucleotides hybridizedwith said target nucleic acids on a second substrate; d) contacting saidtarget nucleic acids with a primer, wherein said target nucleic acidsare amplified upon binding to said primer; and e) detecting the presenceof said target nucleic acids.
 2. The method of claim 1, wherein saidpool of greater than 50 different single stranded oligonucleotides hasbeen produced by: (i) synthesizing greater than 50 different singlestranded oligonucleotides on discrete sites of a first substrate, (ii)releasing said greater than 50 different single strandedoligonucleotides from said first substrate, and (iii) amplifying saidgreater than 50 different single stranded oligonucleotides that arereleased from said first substrate, wherein said releasing andamplifying generates said pool of oligonucleotides.
 3. The method ofclaim 1, wherein said pool of greater than 50 different single strandedoligonucleotides has been produced by: (i) synthesizing greater than 50different single stranded oligonucleotides on discrete sites of a firstsubstrate, (ii) releasing said greater than 50 different single strandedoligonucleotides from said first substrate, and (iii) modifying saidgreater than 50 different single stranded oligonucleotides that arereleased from said first substrate, wherein said releasing and modifyinggenerates said pool of oligonucleotides.
 4. The of claim 1, wherein thediscrete sites are contiguous with other sites.
 5. The method of claim1, wherein the discrete sites are non-contiguous with other sites. 6.The method of claim 1, wherein said greater than 50 different singlestranded oligonucleotides that are linked to said discrete sites on thefirst substrate are linked through a cleavable linker.
 7. The method ofclaim 6, wherein said releasing of said greater than 50 single strandedoligonucleotides from said first substrate comprises cleavage of thecleavable linker with light.
 8. The method of claim 6, wherein saidreleasing of said greater than 50 single stranded oligonucleotides fromsaid first substrate comprises cleavage of the cleavable linker with achemical.
 9. The method of claim 6, wherein said releasing of saidgreater than 50 single stranded oligonucleotides from said firstsubstrate comprises cleavage of the cleavable linker with an enzyme. 10.The method of claim 1, wherein said greater than 50 different singlestranded oligonucleotides in said pool of oligonucleotides are labeled.11. The method of claim 1, wherein said first substrate is selected fromthe group consisting of glass, plastics, polysaccharides, nylon,nitrocellulose, resins, silica, silicon, carbon, and metals.
 12. Themethod of claim 2, wherein said amplifying comprises polymerase chainreaction.
 13. The method of claim 2, wherein said amplifying comprisesrolling circle amplification.